Electrolytic development process for photoconductive copysheets



United States Patent 3,285,837 ELECTROLYTIC DEVELOPMENT PROCESS FOR PHOTOCONDUCTIVE COPYSHEETS Byron W. Neher, Hudson, Wis., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn.,

a corporation of Delaware N0 Drawing. Filed Jan. 9, 1963, Ser. No. 250,226

15 Claims. (Cl. 204-18) This invention relates to an image recording process. In one aspect, the invention relates to a novel electrolytic development technique for photoconductive copysheets. In another aspect, the invention relates to the information of visible dye images on the surface of light exposed photoconductive copysheets.

In one method for developing permanent visible images on photoconductive copysheets, the copysheet is exposed to a light image, then developed electrolytically to deposit a metallic or other visibly distinct material on the more conductive areas of the copysheet surface. Such a process is described in United States Letters Patent 3,010,883. Suitable photoconductive copysheets are also disclosed in United States Letters Patent 3,010,884. In general, the copysheets comprise a photoconductive powder, such as Zinc oxide, bonded to a contiguous electrically conductive backing, usually by an electrically insulative binder. If the electrically conductive backing of the photoconductive copysheet is connected as the anode, it has been found that a rectification effect substantially reduces current passage and makes the electrolytic development difiicult. This rectification effect is not observed when the electrically conductive backing is connected as the cathode, which is therefore the procedure usually employed. However, cathodic electrolytic development gen erally restricts the developer materials to those which are reduced at the cathode, e.g. silver ions to free silver, etc. Many extremely useful oxidizable compounds and materials bearing a net negative charge have therefore not been practically useful in the electrolytic development of light exposed photoconductive copysheets.

In my copending patent application, United States Serial No. 820,254, filed June 15, 1959, now US. Patent No. 3,127,331, a method for eliminating the abovementioned rectification effect is disclosed. This method involves cathodic electrolytic deposition of a free metal on the more conductive portions of the exposed photoconductive sheet, then carrying out another electrolytic reaction with the photoconductive sheet connected as the anode. The presence of the free metal deposit destroysthe rectification barrier and permits current passage in both directions through the photoconductive copysheet. The anodic electrolytic development permits the use of such developers as the leuco form of vat dyestuffs and various colored anions, the latter being exemplified by acid type dyestuffs. However, this technique does require two distinct electrolytic steps.

It is therefore an object of this invention to provide a new method for electrolytic development of photoconductive copysheets.

Another object of this invention is to provide a method for cathodic electrolytic development of photoconductive copysheets using negatively charged developer materials.

A further object of this invention is to provide a method for electrolytic development of photoconductive copysheets in a single step using negatively charged developer materials.

Still another object of this invention is to provide photoconductive copysheets having visible image deposits thereon.

Various other objects and advantages will become apparent from the following disclosure.

3,285,837 Patented Nov. 15,, 1966 "ice In accordance with this invention, it has been found that water soluble anionic dyes, i.e. dyes having a negatively charged chromophore, can be electrolytically deposited from solution onto a cathqdically connected photoconductive copysheet, provided the solution also contains a polyvalent metal ion. The water soluble acid dyes, generally in the form of their sodium or potassium salt, are particularly suitable, the non-mordant acid dyes being preferred. Such acid dyes are generally sulfonic acids of compounds in the nitrophenol, azo, triphenylmethane, anthraquinone, indigoid and other series, the majority being azo, (including polyazo) and anthraquinone dyes. Reactive acid dyes, which contain reactive chlorine that is converted to hydroxyl in alkaline media, e.g. Procion, Cibacron, Drimarene dyes, etc. may be employed. Other reactive dyes include the Remazol and Reactone types. The polyvalent metal ion must, of course, not precipitate or insolubilize the colored anion in the aqueous developer solution. Polyvalent metals selected from Group II of the Periodic Table, particularly magnesium, calcium and zinc, and metals of Group VIII, particularly nickel, are especially preferred, and the use of both magnesium and nickel has provided outstanding results. Water soluble salts of the polyvalent metal ions, e.g. chlorides, nitrates, sulfates, acetates, e'tc.,

may be added to the aqueous bath to provide the polyvalent metal ions.

The actual mechanism by which the water soluble anions are carried to the cathode is not fully understood. When the polyvalent metal ion is not present, the negatively charged dye ions migrate to the positively charged electrode or anode. Since the dyes employed are water soluble, electrophoresis does not seem to be involved. Moreover, complex formation does not appear to be consistent with the experimental data. Whatever the explanation, addition of the polyvalent metal containing ion causes deposition of the dye at the cathode, thereby producing vivid, high contrast, developed images on the photoconductive copysheet surface in a single electrolytic development step without any rectification barrier.

The aqueous developer solutions are generally prepared with up to about one percent by weight of the Water soluble dye and from about 1 to about 5 percent by weight of a metal salt to provide the polyvalent metal containing cation. The dye is preferably first dissolved in the water followed by addition of the metal salt. Various positively charged latex or emulsions particles which are not coagulated by the other constitutents of the developer may also be incorporated into the developer solution. Such latices having positively charged particles,

' e.g. copolymers of vinyl chloride and vinyl acetate, tend Example 1 1% Patent Blue A (CI. 42080) 3 MgCl -6H O 0.5% NiCl -6H O Example 2 1% Pontacyl Fast Violet VR (CI. 45190) 3% Magnesium acetate 0.5 NiCl -6H O 3% sodium acetate Example 3 1% Cibacron Turquoise Blue G 2.5

Example 4 1% Drimarene Black Z-BL 2.5% NiNO -6H O 3 Example 1% Xylene Milling Blue BC (C.I. 42645) 3 0.5% NiCl -6H O 50% ethanol 45.5% water Other suitable dyes which have been used in the abovementioned manner are Chlorantine Fast Turquoise VLL (C.I. 74180), Chlorantine Fast Yellow 4GLL (C.I. 29000), Alizarin Cyanine Green G-CF (C.I. 61570), Basolan Chrome Brilliant Red 3BM (C.I. 45305), Nigrosine B (C.I. 50420), Pontacyl Violet C4BN (C.I. 42650), Alizarin Rubinol 3G-CF (C.I. 68205), Pontamine Sky Blue 6BX (C.I. 24410), duPont Paper Yellow (C.I. 10316), Cibacron Brown 3GR, Cibacron Violet 2R, Cibacron Brilliant Red 3B, Drimarene Red Z-2B, Drimarene Blue Z-RL, Drimarene Black Z-BL, Alizarin Red S (C.I. 58005), and Indigotine. Particularly useful combinations of polyvalent metal and water soluble anionic dye are set forth in Table I.

TABLE I Color Index Acid Dyestuff Polyvalent Index Metal Ion Quinoline Yellow Ni+Mg Paper Yellow L Ni+M Pontacyl Light Yellow GX. N i+Mg Pontamine Sky Blue 6BX N i+Mg Napthol Y low S Ni Metanil Yellow conc N i-l-Mg Pontamine Diazo Blue NA conc N i-M g Pontachrome Azure Blue B cone Ni-Mg Pontachrome Blue EOR Ni-Mg Anthraquinone Blue BN Ni Mg Pontaeyl Green B6 ex. cone Ni-M Pontacyl Brilliant Blue A cone 1 Ni--Mg Pontaeyl Violet C4BN Ni--Mg Croeein Scarlet N ex s. Ni-i-Mg Pontamine Sky Blue Greenish cone Ni-i-Mg Pontarnine Brilliant Blue G conc Ni-l-Mg Pontarnine Test Scarlet 4B5 Ni-i-Mg Pontamine Test Rubine B cone Ni-Mg Drimarene Scarlet Z-GL s. Ni-Mg Drimarene Navy Z-ZRL Ni--Mg Drimarene Golden Yellow ZR.. Ni-Mg Drirnarene Yellow Z3GL Ni-Mg Drimarene Yellow Z-5GL. Ni Mg Drimarene Turquoise Z-G Ni -Mg Drimarene Violet ZRL Ni-Mg Drinlarene Black Z-BL, Ni Mg Drimarene Red ZRL Ni-Mg Drimarene Red Z2B N i--Mg Drimarene Blue ZRL. Ni-Mg Cibacron Yellow R Ni-Mg Oibacron Brilliant Yellow 3G N i-M Cibacron Rubine R Ni-Mg Cibacron Blue 3G Ni+Mg Cibaeron Orange (Brilliant) GP Ni+M Cibacron Brilliant Red B Ni+Mg Cibacron Brilliant Blue BR Ni+Mg Cibacron Turquoise Blue G Zn Cibacron Yellow G Ni+Mg Cibacron Brilliant Violet ZR Ni+Mg Oibacron Brilliant Red 3B Ni+Mg Alizarin Red S Mn Alizarin Red S Ni Alizarin Red S Zn Chlorantine Fast Turquo e VLL Zn+Ni Indig e g Chlorantine Fast Yellow 4GLL Ni+Mg Solophenyl Turquoise Blue GL supra g Alizarin Saphirole B Mg-l-Ni Alizarin Cyanine Green CG Mg+N1 Caleocid Allzarin Green CG. Mg+N1 Azocarmine B Mg+N1 Azocarmine G Mg+N1 Chlorantine Fast Rubine RNLL Zn+Ni Chlorantine Fast Red 5B RL Ni+Mg Basolan Chrome Brilliant Red 3BM- Ni+Zn Patent Blue A Mg-l-Ni N igrosin Ni Pontacyl Violet O4BN N i+Mg Alizarin Rubinol 3G Mg Pontamine Sky Blue 3BX N i+Mg Pontacyl Fast Violet VB. Ni-l-Mg Patent Blue V Ni+Mg Palatine Fast Claret RNT Ni Azo Fuchsine GA ex. conc Ni-i-Mg Erie Anthracene Brilliant Blue 3 G Mg+Ni Paper Yellow OB Mg+Ni Diphenyl Blue Red B Mg+N1 Neptune Green N1+Mg Paper Yellow L N i+Mg are used to provide the cyan, magenta and yellow images,

together providing a full range of color. The following procedures will illustrate useful techniques.

An electrolytically developable photoconductive zinc oxide copysheet was exposed successively to each of three color separation negatives, using contact techniques and a 200 watt projection bulb as light source. The copysheet was electrolytically developed after each exposure, by passing an anodically connected sponge roller over the exposed copysheet surface. The aqueous developer solution carried by the sponge roller contained 1% by weight of the acid dye, 3% magnesium acetate, and 0.5% Nicl -6H O. The dyes used in the three development steps were Du Pont Paper Yellof (C.I. 10316), Pontacyl Fast Violet VR (C.I. 45190), and Pontamine Sky Blue 6BX (C.I. 24410), respectively. After each exposure and development step, the print was rinsed and dried at about C., thereby removing excess developer and effectively erasing the differential photoconductivity pattern on the copysheet before the next exposure. A good full color print was obtained. Satisfactory full color prints can also be prepared from Kodacolor 35 mm. negatives by using a projection system and red, green, and blue filters for the cyan, magenta and yellow development steps respectively.

Images electrolytically produced on photoconductive copysheets in the manner described above can be transferred to separate receptor sheets by diffusion. Transparencies can be prepared by using as a receptor sheet a cellulose acetate backing having a gelatin coating which has been wetted with a dilute acid solution, e.g. a 5 percent acetic acid solution. When the wetted receptor sheet is pressed into contact with the image photoconductive sheet the colored dyes diffuse into the gelatin coating, providing a good quality transparency, usually in about 15 seconds. If the photoconductive copysheet contains a multicolor print thereon, the diffusion techniques can be used to prepare a multicolor transparency. Multiple copies on such receptor sheets can be prepared, the number of copies being limited only by the depletion of dye on the photoconductive copysheet. Separation negatives can be made from positive color transparencies using filters.

Various other embodiments of the present invention will be apparent to those skilled in the art without departing from the scope thereof.

I claim:

1. An electrolytic development process for developing an exposed copysheet having a photoconductive layer on a contiguous electrically conductive backing which comprises contacting the exposed surface of said copysheet with an electrolytically conductive developer solution having dissolved therein an ionizable anionic dye providing a negatively charged chromophore and a polyvalent metal cation selected from the group consisting of nickel, magnesium, zinc and calcium, and electrolyzing said developer solution, the electrically conductive backing of said copysheet being connected to serve as the cathode.

2. An electrolytic development process for developing an exposed copysheet having a photoconductive layer on a contiguous electrically conductive backing which comprises (a) contacting the exposed surface of said copysheet with an electrolytically conductive aqueous developer solution having dissolved therein an acid dye providing a negatively charged chromophore and a salt of a polyvalent metal selected from the group consisting of nickel, magnesium, zinc and calcium, and

(b) electrolyzing said developer solution with the electrically conductive backing of said copysheet being connected to serve as the cathode.

3. The process of claim 2 wherein said polyvalent metal is nickel.

4. The process of claim 2 wherein said polyvalent metal is magnesium.

5. The process of claim 2 wherein said polyvalent metal is zinc.

6. The process of claim 2 wherein said polyvalent metal is calcium.

7. An electrolytic development process for developing an exposed copysheet having a p'hotoconductive layer on a contiguous electrically conductive backing which comprises (a) contacting the exposed surface of said copysheet with an electrolytically conductive aqueous developer solution having dissolved therein an acid dye providing a negatively charged chromophore and a salt of a polyvalent metal selected from the group consisting of nickel, magnesium, zinc and calcium,

(b) electrolyzing said developer solution with the electrically conductive backing of said copysheet being connected to serve as the cathode to develop a visible colored image thereon, and

(c) transferring said visible colored image thereon by diffusion means to an adjacent receptor sheet.

8. The process of claim 7 in which said receptor sheet contains a gelatin coating.

9. The process of claim 7 in which said receptor sheet contains a gelatin coating having a weak acid aqueous solution thereon.

10. An electrolytic development process for developing an exposed copysheet having a photoconductive layer on a contiguous electrically conductive backing which comprises:

(a) contacting the exposed surface of said copysheet with an electrolytically conductive aqueous developer solution having dissolved therein an acid dye providing a negatively charged chromophore and a salt of a polyvalent meta-l selected from the group consisting of nickel, magnesium, zinc and calcium, and

(b) electrolyzing said developer solution with the electrically conductive backing of said copysheet being connected to serve as the cathode to develop a visible colored image thereon,

(c) placing a receptor sheet in contact with said visible colored image and (d) transferring said dye image to said receptor sheet by diffusion means.

11. The process of claim 10 in which said receptor sheet is transparent and the resulting product is a transparency.

12. 'Dhe product obtained by the process of claim 2.

13. The product obtained by the process of claim 7.

14. In the electrolytic development process for developing an exposed photoconductive copysheet the improvement which comprises contacting the exposed surface of said copysheet with an electrolytically conductive developer solution having dissolved therein an acid dye providing a negatively charged chromophore and a polyvalent metal cation selected from the group consisting of nickel, magnesium, zinc and calcium, and electrolyzing said developer solution with said copysheet connected as the cathode.

15. An electrolytic process for preparing a full color reproduction which comprises (a) exposing a panchromatically sensitized photocon- 'ductive copysheet to a light image,

(b) contacting the exposed copysheet surface with an electrolytically conductive developer solution having dissolved therein an ionizable yellow acid type dye providing a negatively charged chromophore and a polyvalent metal cation selected from the group consisting of nickel, magnesium, zinc and calcium,

(c) electrolyzing said developer solution, the copysheet being oonnected as the cathode, thereby developing a yellow image thereon, and

(d) repeating the aforementioned steps with a magenta acid type dye and cyan acid type dye respectively to obtain a full color print on said copysheet.

References Cited by the Examiner UNITED STATES PATENTS 3,057,787 10/1962 Sagura 204-48 3,106,517 10/196 3 Eastman et al 20418 JOHN H. MACK, Primary Examiner.

T. TUFARIELLO, Assistant Examiner. 

1. AN ELECTROLYTIC DEVELOPMENT PROCESS FOR DEVELOPING AN EXPOSED COPYSHEET HAVING A PHOTOCONDUCTIVE LAYER ON A CONTIGUOUS ELECTRICALLY CONDUCTIVE BACKING WHICH COMPRISES CONTACTING THE EXPOSED SURFACE OF SAID COPYSHEET WITH AN ELECTROLYTICALLY CONDUCTIVE DEVELOPER SOLUTION HAVING DISSOLVED THEREIN AN IONIZABLE ANIONIC DYE PROVIDING A NEGATIVELY CHARGED CHROMOPHORE AND A POLYVALENT METAL CATION SELECTED FROM THE GROUP CONSISTING OF NICKEL, MAGNESIUM, ZINC AND CALCIUM, AND ELECTROLYZING SAID DEVELOPER SOLUTION, THE ELECTRICALLY CONDUCTIVE BACKING OF SAID COPYSHEET BEING CONNECTED TO SERVE AS THE CATHODE. 